Compare the dates of birth
An age difference is the distance between two birth dates. You do not need to calculate each person's age today and subtract the displayed years and months. That approach can introduce rounding and month-length problems. Comparing the birth dates directly gives a stable interval that does not change at midnight or on either person's birthday.
Our tool accepts the dates in either order. It places them in chronological order before calculating and shows both dates in the result. You can use this with siblings, friends or historical figures without supplying anyone's name.
A simple example
Suppose one person was born on 10 March 1990 and another on 25 August 1992. Two full years bring the earlier date to 10 March 1992. Five months bring it to 10 August, and another 15 days reach 25 August. The result is 2 years, 5 months and 15 days.
Same birthday, different years
When the month and day match, the difference is usually a whole number of calendar years. The total days can vary depending on how many leap days lie between the dates. For example, the day count across four calendar years can include a leap day. That is why multiplying the displayed years by 365 does not always reproduce the total days.
Dates near a month boundary
For uneven month lengths, our calculation uses the same forward-counting convention as the exact age tool. It counts completed years, then completed months, clamping an unavailable month-end day, and then counts the remaining days. The separate total-days result counts the actual date boundaries crossed.
What the answer can tell you
The interval is useful for family records, timelines and everyday comparisons. A label such as “same generation” is a separate interpretation, with no universal age-gap cutoff. We display the dates and arithmetic so you can apply the result to your own purpose.
For a school entry date or another formal condition, inspect each person's age on the actual cutoff date with the main age calculator. A fixed gap between two people does not tell you whether either meets the particular condition on that date.